Method for making phenol



w 20 15 R. H. KRIEBLE Er AL,

ETHOD FOR MAKING PHENOL Filed Nov. so.. 1944 K Nw .All

INE un ied by n-hexene Patented Apr.y 20, 1948 haben n. mienne,v William I. Denton, to Socony-Vacunm Scliencctmiv,"` Woodbury, N. J.. assignors Oil Company, `Incorporated,

N. Y., and

a corporation of New York Application November 30, 1944, Serial No. 565,927

1 1 (ilaims.l

This invention has to do with the production of phenol by the oxidation of benzene and is more particularly concerned with that type of process wherein a reaction mixture consisting of benzene f and oxygen or molecular oxygen-containing gas suchas airis passed through a reaction zone voidI of solid catalyst, under pressure and at elevated temperature.

This application is a continuation-impart of our copending application Serial No. 465,411, filed November 13, 1942, now abandoned, which, in turn, is a continuation of our application Serial No. 395,016, filed May 24, 1941, now abandoned.

We are aware of the fact that processes of this general character have heretofore been proposed,

, and in this regard, reference is made to the Bone et al. Patent No. 2,199,585 and the Moyer et al. Patent No. 2,223,383. Each of these patents discloses a process of the general character above referred to, and each mentions that the process therein disclosed can be carried out by recycling. We have discovered, however, that although the process of Bone, for example, if used with a relatively impure grade of commercial benzene, can,

be operated to obtain a fair yield of phenol on a small number of passes in a recyclingl operation, the conversion to phenol rapidly decreases with successive cycles, thus materially restricting the scope of the process and rendering it impractical `as a recycle operation. We have also observed that if a chemically pure (reagent grade) of benzene is subjected to the process of the Bone patent, no substantial conversion to phenol is obtained.

Since the percentage conversion of` benzene to phenol in an oxidation process of the class described is relatively small, it is obviously essential from the standpoint of practicability that the operation be one in which the unconverted benzene can be continuously recycled with a substan-4 tiallyconstant conversion and yield of phenol under a given set of operating conditions. It is the primary object of this invention to provide such a process.

As described in our application Serial No. 395,016, referred to above, various compounds,

which will react with oxygen to form water at a lower temperature than that at which benzene will react with oxygen to form water, under the conditions of reaction in the process contemplated therein, act as promoters or inductors in the oxidation of benzene to phenol and other oxidation products. Glenn-containing hydrocarbons typiand cracked gasoline, are disclosed therein as one oi several groups of `coin- (ci. eso-621) pounds covered by the foregoing classication and thus effective in the oxidation of benzene to phenol and other oxidation products. The oleiins form the subject matter of this application. 3 This invention is predicated upon the discovery that a minor proportion of an olen, and particularly a cracked gasoline which contains an olefin or olens, added to benzene substantially improves the conversion to, and yield of, phenol from benzene under the conditions of reaction in the process contemplated herein, over the conversion and yield obtained without said olen. The present invention is also predicated upon the related discovery that if a minor proportion of an 16 olefin, and particularly a cracked gasoline, is continuously introduced into the stream of benzene entering the reaction mixture, the conversion to, and yield of, phenol from benzeneis appreciably increased over the conversion and yield obtained 20 without said olen.

For the continuous operation contemplated herein a properly proportioned mixture of benzene and air, or other oxygen-containing gas, is

thoroughly mixed and pre-heated to the desired,

26 temperature and passed through a reactor tube which has been pre-heated and which for the purpose of pre-heating and dissipating the heat of the exothermic reaction is immersed in a suitable heat-tran'sfer bath, such as salt. The reaction mixture, as will hereinafter be explained, is preferablyl maintained under pressure. With properly regulated conditions a part of the benzene is thus oxidized to phenol. This phenol and the gaseous and high-boiling products of oxidation are then separated from the benzene, which is subsequently recycled throughthe mixer-preheater and reactor. Additional air is of course added prior to the admission of the benzene to the pre-heater-mixer, and in a continuous operthe benzene converted.

In such an operation we have found that where a commercial grade of benzene, such as-90% benzol," is used as the charging-stock and is recycled through the reactor with no additions of make-up stock under xed conditions of temperature and pressure, the benzene rapidly loses its reactivity and, further, that the reactivity may be restored only in part through altering the reacting conditions by going to higher temperatures. The charge eventually becomes unreactive even at relatively high temperatures. We have Aalso found that when the procedure just described above is altered by adding fresh benzene to merely make-up the benzene converted,

ation make-up benzene is also added to replace.

the reactivity fand conversion to phenol is not markedly increased. However, in'an operation of the recycle type Just described, if a minor proportion of an `oleiin, such as n-hexene or a cracked gasoline containing an oleiln or olens, is continuously added to the charge of benzene, a steady conversion perfomance may be obtained and the reactivity, as indicated by the per cent conversion and yield ci phenol at a given temperature, is greatly increased. We have found that the reactivity in a process of the class described under a given set of conditions may be greatly increased by the incorporation in the reaction mixture of a minor proportion of an olefin.

As indicated above, no substantial conversion of a chemically pure (reagent grade) benzene to phenol takes place in the process contemplated herein. The results provided below in Table I serve to illustrate the improvement realized by the use .of an `oleiin inthe oxidation of benzene to phenol. The single-pass runs were made with reagent grade benzene in a carbon steel tube 15' long and 0.21 inside diameter, at 1000 pounds per square inch and at a reaction time of about 35 seconds with the approximate mixture High boiling products obtained in the runs are designated as H. Bs in the table. The cracked gasoline used has the following properties:

Specific gravity 0.703 Aniline number (F.) 105 Norwood bromine addition number (gms.

Br./l gms. gasoline) 92.6 A. S. T. M. distillation:

I. B. Pt (F) 98 124 50% 169 90% 235 E. Pt. 260

Table l' V Weight Per Cent Conversion Inductor Per Cent 'ggg' Loss to Phenol H Bfe. oxides 0f Carbon None S25 o. 1 i. 0 0. 2 None 900 0.4 1.3 0.3 Cracked Gasoline 1Z0 825 2. 0 3. 0 o. e n Hexene l u 850 2.0 1.9 0.8

It is readily seen that small, and almost negligible, conversions of benzene to phenol are effected when reagent grade benzene is used alone; and, where n-hexene'and cracked gasoline are used, appreciable conversions are eiected. Although the conversions with these preferred inductors are only of the order of about 3%, such conversions may be maintained in a continuous operation by maintaining the proper promoter concentration in each pass.

While the relatively impure commercial benzene contains as impurities compounds which promote the reaction, the concentration of these promoters is not sumciently great to permit successful continuous operation. strated by the following data: continuous runs were made with the 90% benzol of commerce under operating conditions of '750 pounds per square inch, 840 F., 8.5 seconds reaction time, and a benzene to oxygen molecular ratio of about 4:1. In one run, a fresh feed of 1.7 liters per hour of 90% benzol" was used.

Two comparative 4 After 'Z1/2 hours, a material balance was taken. The yield of phenol obtained was 24% and the y per pass conversion of benzene to phenolwas This is demon- 0.81%. That the impurities in the fresh feed did not maintain the conversion at a high enough level to use up al1 of the fresh feed is shown by the low yield oi phenol. low conversion of benzene to phenol, and bythe fact that the recycle benzene increased by 5.7 liters, an amount equal to about half of the benzene added. Therefore, in a second run of 'Z1/2 hours the benzene added as fresh feed was cut in half (0.9 liter per hour). The uitimate yield was only 9%, the per pass conversion to `phenol only 0.27% and the recycle benzene again increased. The results of these runs clearly reveal the normal impurities in commercial benzol are not suflicient to maintain a satisfactory promoter concentration during recycle operation.

While only very small yields of, and conversions of benzene to, phenol are obtained with 90% benzol in a true recycling operation, it is to be understood that true recycling operation is contemplated herein. For example, substantial yields of phenol are obtained in a true recycling" operation when benzene-containing charges having a sufdcient promoter concentration are used. Illustrative of such an operation is the following: Conditions of pressure, temperature, reaction time and benzene to oxygen molecular ratio were 750 pounds per square inch, 840 F., 8.5 seconds and about 4:1, respectively. The charge was a mixture of 85.7 volume per |cent of 90% benzol and 14.3 volume per cent of cracked gasoline, giving a promoter concentration in the reactor feed of about 21/2 per cent. The ultimate yield of phenol was 32 weight per cent at a per pass conversion of 4.5 weight per cent. That a true recycling operation was obtained is evidenced by the fact that the amount oi recycle stock in the system remained constant during the continuous run.

Although we do not wish to be bound by any theory as to the mechanism of this reaction or the part which the olefin plays in increasing the reactivity and conversion to phenol, it is our view that the mechanism as represented by the following equations will explain most of the observed facts:

Reaction I is slow and determines the rate. Reactions II and III, since they involve radicals, should be extremely rapid. Reaction III is shown as a competition of phenyl and hydroxyl radicals for phenyl and is probably over simplified. The essential fact is that in the presence of a material which can be more readily dehydrogenated by 0n than benzene, H02 is produced independently of reaction I and at a lower temperature. It is then capable of reacting rapidly with benzene by reactions II and III to produce the usual products. The presence of the radical H02 has been reported by several workers investigating hydrocarbon oxidation [see W. Jost, Explosion and- Combustion Processes in Ga-s," 409, McGraw-Hill Book Company, Inc. (1946) translated by Huber 49, 2763 (1927); J. Phys. Chem., 29, 1140 (1925); J. Weiss, Trans. Faraday Soc., 42, 133 (1946); P. George, ibid., 42, 210 (1946); George and Robertson, ibid., 42, 217 (1946); W. A. Waters, ibid., 42, 281 (1946); H. W. Melville, ibid., 42, 317 (1946); Style and Summers, ibid., 42, 393 (1946) l.

Under these conditions, far more phenol survives, less diphenyl is formed, and the yield is greatly improved.

According to the foregoing mechanism, then, an Inductor or promoter for use in a process of the type contemplated herein is any compound which is a better hydrogen donor than benzene under the conditions of the reaction zone; or, stated in another way, a promoter or inductor may be dened as a compound containing hydrogen and possessing the properties of being in the gaseous phase under the conditions of the reaction zone, and under said conditions, reacting with oxygen to form water at a lower temperature than the temperature at which benzene so reacts with oxygen.

Of the oleiins and olen-containing hydrocarbons, n-hexene and olefin-containing cracked gasclines are particularly preferred.

As stated hereinabove, the promoters contemplated by the present invention are better hydrogen donors than benzene under the conditions of the reaction zone. In other words, the promoters in our process are hydrogen-containing materials which release hydrogen more readily than benzene under the conditions of reaction. The rates of hydrogen release from numerous materials are available in the chemical literature and may be resorted to in selecting effective promoting materials. From such data we have derived potential hydrogen donor ability" (P. H. D. A.) values for various materials and have foundthose materials having values above a cer- 'tain minimum are effective in our process. The

P. H. D. A. value relationship thus provides a means whereby a chemist skilled in the art may readily determine, with a high degree of certainty, whether or not a material will be an effective promoter. i

The P. H. D. A. values obtained for various materials are derived in the following manner. Hydrogen atoms are classied here into four categories: primary, secondary, tertiary and hydrogens attached to an olefinic bond or an aromatic ring. No attempt has been made to evaluate bonds other than the carbon-hydrogen bond. With this as a starting point and taking activation energy values from the chemical literature, it is possible to evaluate relative ratios of release of the dierent hydrogen atoms from hydrogencontaining materials. Average activation energy values taken from The Aliphatic Free Radicals (F. O. Rice and O. K. Rice, Johns Hopkins Press; 1935) Vare as follows:

Relative rates of hydrogen release under conditions typical of our process, as at 427 C., are calculated from the well-known relationship E K= ce RT wherein K is the specific velocity constant; C is a constant; E represents 'activation energy (in calories); Ris a constant (1.987 calories): and T is absolute temperature (in degrees Kelvin). The relative rate of a primary hydrogen atom as compared with an olenic hydrogen atom is calculated as follows:

K. 6000 l .21 c--e 2(427-5-2 3) 10g X427 y-:1.864

In this manner it is found that the several hydrogen atoms have the following K values at 427 C.:

Oleiinic (aromatic) 1 Primary 73 Secondary y 215 Tertiary ---s ---1. 1280 The foregoingKarc. values indicate that a primary hydrogen atom is released 73 times faster than an oleflnic or aromatic hydrogen atom. Simplifying this relationship by assigning a zero (0) value to an oleflnic or aromatic hydrogen atom and a value of one (1) to a primary hydrogen atom, the following values obtain:

Olenic (aromatic) 0 Primary 1 Secondary 3 Tertiary 15 it depends largely upon the structure of the-mole- V n cule. It is recognized that different substituent groups such as olefin, ketone, ester, ether, etc., groups may activate hydrogen atoms to diierent degrees. For convenience, however, a constant value has been assigned to such activation. Accordingly, whenever a primary hydrogen is in an activated position, it is assigned a value equivalent to a normal secondary hydrogen. Similarly, an activated secondary hydrogen atom is assigned a value equivalent to a normal tertiary hydrogen atom; and for an activated tertiary hydrogen atom, the normal rate is doubled.- The P. H. D. A. of a compound, on a weight basis, is the sum of all the evaluated hydrogen atoms multiplied by a factor of ten and divided by the molecular Weight of the compound. x

From the Km c. values of 0, 1, 3 and 15 shown above, the P. H. D. A. values of hydrogen-containing materials are easily calculated. By way of illustrations, n-hexene-l has three primary, four secondary and two activated secondary (alpha to an olen bond) hydrogen atoms, and three inactive hydrogen atoms, the latter being attached to an olefin bond; therefore, n-hexene-l has a P. H, D. A. value, on a Weight basis of 5.4

Illustrative of materials found to'be ineffective experimentally and as indicated by its P.l H. D. A. value is ethyl alcohol. This compound has three primary and two secondary hydrogen atoms, and has a P. H. D. A. value, on a weight basis, of 2.0.

The P. H. D. A. values for materials tried in our process as promoters are in substantial agreement with the experimental results obtained. However, in the case of flrst members of the various chemical classes which often behave diiierently than Iall other members of their `classes, some discrepancies obtain between the tiveness. This relationship isxshown in the iollowing tabulation:

anni. Compound (Weight) carbon disulde g 2.0 2.0 1.o 1.7 4.2 3.5 5.4 4.4 as 5.4 ao 5.5 9.o an 8.9 2.7

As will be readily apparent to those skilled in the art, the apparatus used in carrying out a process ofthe type contemplated herein may take various forms. In the accompanying drawings, however, we have shown diagrammatically one form of apparatus which may be satisfactorily used in carrying out an operation for the continuous conversion of benzene to phenol. As will hereinafter appear, the conditions of operation embodyga number of variables which may be changed with respect to one another over relatively wideflimits. and no attempt will be made in describing the apparatus to take accpunt of these possible changes in variables.

Referring now to the drawing, reference numerals II and II indicate conduits which carry benzene and are connected through suitable valves I2 and I2' with the inlet I3 of a pump I4. The pump I4 delivers the benzene through a conduit I5 to a T-connection I6, where it is introduced into a mixing conduit I1 leading to the f coils I8 of a mixer and pre-heater mounted in an insulated case I9 which is filled with a suitable heat-exchange medium such as Dowtherm.

Reference numeral 20'indicates an air-com- 4pressor which discharges into pipe 2| connected through the connection 212 to a compressed-air storage reservoir 23. The pipe 2I discharges through a pressure-reducing valve 24 and an ori iice now-control 25 into the conduit I1, through which the air-and-benzene reaction mixture is conducted to the mixing and pre-heating coil I8.

The inductor or promoter is introduced into the reaction mixture at any suitable point, preferably in the benzene stream, through a conduit as indicated by numeral 28, such conduit being provided with a metering valve 29 to control the quantity of an inductor, such as a cracked gasoline, which is introduced.

mixed and pre-heated to a temperature below the temperature at which reactions will take place, discharges into a header 40, which connects with a series of reactor tubes 4I. The reactor tubes are suspended in a suitable heat-transfer bath, such as a fused salt bath, capable of maintaining a close temperature control, such bath being contained in the insulated case 42, which is provided with an inlet conduit 43 having a pump 44, the inlet 45 of which connects with a heat-exchanger 46 which can be used to raise the temperature of the salt bath for initiating the reaction and, after the exothermic reaction has started, can be vused to dissipate the heat of reaction and maintains constant temperature. The heat-exchanger 46 receives the heat-exchange medium from the tank 42 through a discharge conduit 41.

In the form of the apparatus shown in the drawing, the reactor tubes are illustrated as being U-shaped, and the discharge portion 4I' of the respective reactor tubes connect with a header conduit 50 which discharges into the coil 5I of a heat-exchanger 52. For the thermal balance of the process this heat-exchanger 52 is shown as being connected through conduits 53 and 54 with the mixer and pre-heater I9 so that the heat-exchange medium is circulated by ,means of pump 55 from the bottom of the mixer and preheater I9 to the bottom of the heat-exthrough the pipe 53.

The cooled. reaction mixture containing the phenol and other products of the reactiondis charges from the heat-exchanger 52 through pipe 56-56' and iilter 51 into a high-pressure mistbreaking tower 5B having a high-pressure gasdischarge valve 59 which may lead to a turbine. Discharge valve 59 is controlled by orifice ilowcontrol Z5 to maintain a constant flow of air in pipe I1. The liquid product accumulating in the bottom of the high-pressure tower 58 is conducted through a pressure-reducing valve 60 into a loW-pressure-packed tower 5I provided with a valved vent 62 to release gaseous products. The liquid Aproduct collecting in the bottom of towell 6I is discharged through conduit 5 I This liquid product. which is a mixture of phenol, benzene, and high-boilers, is delivered to the benzenerecovery still 62. In the still, as illustrated, the liquid products pass through a pre-heater 63 and are discharged through the discharge pipe 63 into the bottom of the still 62, where the benzene is distilled oi by a steam coil reboiler 64. The still 62 is shown as being equipped with bubble plates 65 and a water coil reux-.condenser 65'. The benzene vapors are discharged through conduit 66 into a benzene condenser 56', from which the liquid product discharged through conduit 51 is pumped by means of pump B8 into abenzenewashing tower 69. from which the recycle benzene enters the benzene conduit II'.

The bottom of the benzene-recovery still 62 is vprovided with a discharge conduit 10 through 'phenol-discharge pipe 18 connected with a The pre-heatingl and mixing coil I8, wherein the benzene-promoter-air mixture is intimately phenol-discharge pump 19. The high-boiling products of oxidation, which are referred to as high-boilers, are discharged from the still 1l through the conduit .80 by means of a pump'al.

As has been previously pointed out, the process contemplated herein embodies a number of variables which are susceptible of adjustment With'respect to one another to obtain optimum operating conditions for a given set of variables. lThese variables include: the ratio of oxygen and benzene in the reaction mixture; the reaction time; the pressure under which the operation is carried out; the temperature of reaction: the material, internal diameter and length Aof the reactor tube; the internal diameter and length of the pre-heater coil and the temperature of the pre-heater bath; and the olen used as the inductor and the proportions in which it is used.

In order that some indication may be afforded as to the eifect of these variables, each of them will now be discussed individually.

The proportion of air that can be used to advantage in the reaction mixture has a maximum and a minimum limit that varies with the conditions used and with the internal diameter of the reactor tube (4 |-4|) l Preferred operating conditions with 0.36 inch reactor tubes, for example, include a benzene to oxygen ratio of from 2.521 to 8:1, and particularly a ratio of 4:1. In terms of air then, the

most preferred ratio is 4CsHsIlO2r4N2.

Reaction time For the purpose of this discussion, the reaction time may be deiined as the time taken for a molecule of the reaction mixture to pass through' varies with the apparatus and the conditions ofv use. Above this so-called critical minimum value, an increase in reaction time can be compensated for by a small decrease in reaction temperature. However, for reaction times below the minimum value, there is a sharp rise in the production of high-boilers and a corresponding decline in phenol yield although the actual conversion to phenol is not greatly affected. The value of this so-called critical minimum reaction time, as aforesaid, is dependent upon the apparatus and conditions of use, and it is probable that the controlling factor rests in the ability of the apparatus to dissipate heat. As preferred, the reaction time should fall within the range of 2 seconds to about 100 seconds.

The optimum reaction time is about 8.5 seconds under the following preferred operating conditions:

Charge: 90% Benzene having added thereto about 15% (by volume) of a cracked gasoline.

Reactor: 0.36` inch internal diameter stainless steel tube 60 feet long.

?ressure: 750 pounds per square inch. Femperature: 840 F.

Pressure We have obtained phenol in good conversion at irlessures of from 60 pounds per square inch to 000 pounds per square inch. The higher the ressure, the lower the optimum reactor temerature, other conditions being the same. Thus,

italyze total combustion at temperatures above good results have been obtainedin nickel tubes at a, pressure of 350 pounds per square inch where the'optimum reaction temperature was about 1030 F., and probably still lower pressures and higher temperatures could have been successfully used. With iron tubes, suicient pressure to keep the reaction temperaturebelowi 1000 F. is required, usually atleast 500-1000 pounds per square inch. However, at 1000 pounds pressure, the use of nickel tubes instead of iron or stainless steel tubes presents no advantage.

The use of high pressure has certain fundamental advantages, however. At low pressures, even though' a glass-lined reactor be used, the loss to oxides oi. carbon is materially higher than at high pressures in stainless steel equipment. Furthermore, the minimum critical reaction time apparently increases with decreasing pressure; and, since for a constant reaction time the rate of feed varies directly with the pressure (by dennition), the maximum permissible rate of throughput falls oil` very rapidly with decreasing pressure.

There is also an upper useful limit of pressure. As the pressure is raised, the temperature required to initiatereaction decreases, as explained above. is raised until the critical temperature of liquid benzene (550 F.) is reached, where it remains unchanged as the pressure is further increased. Since it is advantageous to mix thoroughly the benzene vapor and air before initiating reaction, in order that local regions of undesirably high oxygen-concentration be eliminated. it is not desirable to indefinitely lower the reaction temperature by the use of extremely high pressures. There is a relationship between the maximum useful pressure and the internal diameter of the reactor tube, since we have found that the smaller theA internal diameter of the reactor tube, the higher the action. In a 0.36 inch internal diameter reactor tube, 1500 pounds per square inch appears lto be about the upper useful limit, and we prefer a pressure of about 750 pounds per square inch. In general, however, pressures within the range of about 350 pounds to about 1500 pounds per square inch serve the purposes of this invention.

Temperature Reactor tvube As we have previously indicated, it is highly desirable that the reactor tube be void of solid catalyst and that it be of a materialwhich will have no substantial catalyzing effect in accelerating the oxidation of benzene. We have observed in this connection that the chief effect of a solid catalyst is to increase the loss to total-combustion products and therefore to be avoided in the reactor tube (4I-4P). At the relatively high temperatures encountered in low-pressure oxidation, the use of extremely inert (non-catalytic)` inner surfaces of the reactor tubes, such as glass,

Furthermore, the boiling point of benzene temperature necessary to initiate reper cent by volume, that At moderate pressures (several hundred pounds 4- per square inch), nickel is satisfactory. At pressures in the neighborhood of i000 pounds per square inch, low-carbon steel and stainless steel are satisfactory, and nickel presents no advantage.

As to the internal diameter of the reactor tube (4l-IV) successful operation has been obtained in tubes varying from 0.080 inch to 0.875 inch in internal diameter. For iron tubes, the smaller the internal diameter the higher the required pressure. We prefer to use a tube having au internal diameter in thenelghborhood of 0.36 inch and to operate with pressures in the range of from 350 to 1500 pounds per square inch. Smaller tubes are equally satisfactory, but they require higher operating pressures. For a tube having an internal diameter oi 0.086 inch, pressures of from 2000 pounds to 3000 pounds per square inch are recommended.

The llength of the reactor tube (4i-4V) apparently determines the rate of throughput, and the existence of a critical minimum reaction time for a tube of iixed length and internal diameter has already been discussed. Satisfactory results in the operation of a process of the class described have been obtained with tube lengths of 15 feet, and tubes of at least this length are recommended.

Mixer-pre-heuter tube As to the mixer-pre-heater tube (I) any material having suitable mechanical properties such as stainless steel is satisfactory, The internal diameter of this tube should be sufficiently small to prevent reaction taking place therein, and the tube should be suiilciently long to provide the Inductor 1 The required properties of the inductors and the theory of their action, together with certain preferences therein to n-hexene and cracked gasolines and the like, have already been discussed.

The concentration of the inductor may be varied depending upon the character of the makeup stock, the conditions of operations, etc. With a cracked gasoline, which is a preferred inductor, We have found that this concentration should be maintained in the neighborhood of from about 2 per cent to about 35 per cent by volume, based upon the quantity of benzene in the fresh feed; such concentrations represent about 1 to about 51,/2 volume per cent of promoter in the total feed, including the promoters already present in commercial benzene. We prefer, however, to use a concentration of cracked gasoline of about 15 is, about 2/z volume per cent of promoter in the total feed. In general, however, olefin concentrations from about 0.25 per cent to about 5 percent, by volume, of the total feed make for satisfactory results in the making of phenol as hereinabove described.

It will be seen from the foregoing discussion that a process of the'type contemplated herein is susceptible of numerous operating conditions through manipulation of the variables discussed; and the present invention is not concerned with any particular set of operating conditions, but

as aforesaid. is predicated upon the discovery that greatly improved results and a continuous recycling operation may be obtained by introducing into the reaction. mixture an inductor or prometing compound of the type hereinabove discussed. It is to be understood, therefore, that although we have described and illustrated a specific form of apparatus and have discussed' in considerable detail various reaction conditions which may be employed in the operation of such apparatus, the invention is not limited to this apparatus or to any particular set of operating conditions, but includes within its scope such changes and modifications as fairly come within the spirit of the appended claims.

We claim:

l. In the method of making phenol wherein a reaction mixture of benzene vapor and oxygencontaining gas is passed under a pressure in excess of about 500 pounds per square inch through a reaction zone at a temperature between about 600 F. and about 950 F., said reaction Zone having a metallic surface and being void ofsolid catalyst, the step of incorporating in the reaction mixture an oleiin-containing hydrocarbon having a potential hydrogen donor ability value greater than about 2.5, in an amount such that the olen concentration of the reaction mixture is within the range of from about 0.25 vper cent to about 5 per cent by volume.

2. In the method of making phenol wherein a reaction mixture of benzene vapor and oxygencontaining gas is passed under a pressure in excess of about 500 pounds per square inch through a reaction zone at a temperature between about 600 F. and about` 950 F., said reaction zone having a metallic surface and being void of solid catalyst, the step of incorporating 1n the reaction mixture an olefin-containing hydrocarbon fraction having a potential hydrogen donor ability" value greater than about 2.5, in an amount such that the olein concentration of the reaction mixture is within the range of from about 0.25 per cent to about 5 per cent by volume.

3. In the method oi. making phenol wherein a reaction mixture of benzene vapor and oxygencontaining gas is passed under-a pressure in excess of about 500 pounds per square inch through a reaction zone at a temperature between about 600 F. and about 950 F., said reaction zone having a metallic surface and being void of solid catalyst, the step of incorporating in the reaction mixture an olefin-containing cracked gasoline having a potential hydrogen donor ability value greater than about 2.5, in an amount such that the olefin concentration of the reaction mixture is within the range of from about 0.25 per cent to about 5 per cent by volum'e.

4. In the method of making phenol wherein a reaction mixture of benzene vapor and oxygencontaining gas is passed under a pressure in excess of about 500 pounds per square inch through a reaction zone at a temperature between about 600 F. and about 950 F., said reaction zone having a metallic surface and being void of solid catalyst, the step of incorporating in the reaction` mix-ture an olefin having a potential hydrogen donor ability value gre'ater than about 2.5, in an amount such that the olen concentration o! the reaction mixture is within the range of from about 0.25 per cent to about 5 per cent by volume.

5. In the method a reaction mixture of benzene containing gas is passed under a of making phenol wherein vapor and oxygenpressure in in thereaction mixture n-hexene-l in an amount such that the olefin concentration of the reaction mixture is within the range of from about 0.25 per cent to about per cent by volume. l 6. In a method for thecontinuous manufacture of phenol from benzene wherein a reaction mixture of benzene vapor.' and oxygen-containing gas is passed under a pressure in excess of about 500 pounds per square inch through a reaction zone at a temperature between about 600 F. and about 950 F. to convert a part of the benzene to phenol and other oxidation products, and wherein unconverted benzene is separated from the phenol and other oxidation products and is returned for recycling in the reaction mixture, said reactionI zone having a metallic surface and being void of solid catalyst; the i'nprovement which comprises continuously incorporating in the benzene so recycled, prior to its admission to the reaction zone, an olencontaining hydrocarbon having a potential hydrogen donor ability value greater than about 2.5, in an amount such that the olefin concentration of said reaction mixture is within the range of from about 0.25 per cent to about 5 per cent by volume.

'7. In a method for the continuous manufacture of phenol from benzene wherein a reaction mixture of benzene vapor and oxygen-containing gas is passed under a pressure in excess of about 500 pounds per square inch through a reaction zone at a temperature between about 600 F. and about 950 F. to convert a part of the benzene to phenol and other oxidation products, and wherein unconverted benzene is separated from phenol and other oxidation products and is returned for recycling in the reaction mixture, said reaction zone having a metallic surface and .being void of solid catalyst; the

improvement which comprises continuously in-` taining hydrocarbon fraction Ahaving a potential hydrogen donor ability value greater than about 2.5. in an amount such that the olefin concentration of said reaction mixture is within the range of from about`0.25 per cent to about 5 per cent by volume. Y

8. In a method for the continuous manufacture of phenol from benzene wherein a reaction mixture of benzene vapor and oxygen-containing gas is passed under a pressure in excess of about 500 pounds per square inch through a reaction zone at a temperature between about 600 F. and about 950 F. to convert a part ol' the benzene to phenol and other oxidation products, and wherein unconverted benzene is separated from phenol and other oxidation products and is returned for recycling in the reaction mixture, said reaction zone having a metallic surface and being void of solid catalyst; the improvement which comprises continuously incorporating in the benzene so recycled, prior to its admission to the reaction zone. an olefincontaining cracked gasoline having a potential hydrogen donor ability value greater than about 9. In a method for the continuous manufacture of phenol from benzene wherein a reaction mixture of benzene vapor and oxygen-con taining gas is passed under a pressure in excess of about 500 pounds per square inch through a reaction zone at a temperature between about 600 F. and about 950"v F. to convert a part of the benzene to phenol and other oxidation prod` ucts, and wherein unconverted benzene is separated from phenol and other oxidation products and is returned for recycling in the reaction mixture, said reaction zone having a metallic surface and being void of solid catalyst; the improvement which comprises continuously incorporating in the benzene so. recycled, prior to its admission to the reaction zone, an olefin hav- 600F. and about 950 F. to convert a part of 2.5, in an amount such that the olefin concenthe benzene to phenol and other oxidation products, and wherein unconverted benzene is separatedirom phenol and other oxidation products and -is returned for recycling in the reaction mixture, said reaction zone having a metallic surface and being void of solid catalysts; the improvement which comprises continuously incorporating in the benzene so recycled, prior to its admission to the reaction zone, n'heXene-l in an amount such that the olen concentration,

of said reaction mixture is within the range of from about 0.25 per cent to about 5 per cent.

ll. The continuous method for the manufacture of phenol from benzene which comprises passing a reaction mixture of benzene and oxygen-containing gas through a reaction zone havl ing a metallic surface and being void of solid catalyst, under a pressure in -excess of about 500 pounds per square inch, and at a temperature between about 600 F. and about 950 F., said reaction mixture having an olefin concentration ranging from about 0.25 per cent to about 5 per cent; separating from the products of reaction unconverted benzene and phenol substantially iree of unconverted benzene; recycling unconverted benzene with a quantity of fresh benzene suiiicient to replace benzene converted in the previous passage through said reaction zone, and with oxygen-containing gas; and continuously incorporating with the recycle charge, prior to its reaction in said reaction zone, an olefincontaining hydrocarbon having a potential hydrogen donor ability value greater than about 2.5, in an amount such that the olefin concentration of the recycle charge is within the range of from about 0.25 per cent to about 5 per cent by volume.

ROBERT H. KRIEBLE. WILLIAM I. BENTON,

REFERENCES CITED Name Date Moyer Dee. 3. 1940 Number 

